1、Designation: D 2275 01An American National StandardStandard Test Method forVoltage Endurance of Solid Electrical Insulating MaterialsSubjected to Partial Discharges (Corona) on the Surface1This standard is issued under the fixed designation D 2275; the number immediately following the designation in
2、dicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method differentiates among s
3、olid electricalinsulating materials for use at commercial power frequencieswith respect to their voltage endurance under the action ofcorona (see Note 1). In general, this test method is moremeaningful for rating materials with respect to their resistanceto prolonged a-c stress under corona conditio
4、ns than is dielec-tric strength.NOTE 1The term “corona” is used almost exclusively in this testmethod instead of “partial discharge”, because it is a visible glow at theedge of the smaller electrode. This is a difference in location, not in kind.Partial discharges also occur at the edges of electrod
5、es, and in generalcorona describes an electrical discharge irrespective of its location.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns, if any, associ
6、ated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements, see Section 7.2. Referenced Documents2.1 ASTM Standards:D 149 Test Met
7、hod for Dielectric Breakdown Voltage andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power Frequencies2D 1711 Terminology Relating to Electrical Insulation2D 1868 Test Method for Detection and Measurement ofPartial Discharge (Corona) Pulses in Evaluation of Insu-lation S
8、ystems2D 5032 Practice for Maintaining Constant Relative Humid-ity by Means of Aqueous Glycerin Solutions3D 6054 Practice for Conditioning Electrical Insulating Ma-terials for Testing4E41 Terminology Relating to Conditioning4E 104 Practice for Maintaining Constant Relative Humidityby Means of Aqueou
9、s Solutions5E 171 Specification for Standard Atmospheres for Condi-tioning and Testing Flexible Barrier Materials62.2 Special Technical Publications:Symposium on Corona, STP 198, ASTM, 1956.7Corona Measurement and Interpretation, Engineering Di-electrics, Vol 1, STP 669, ASTM, 1979.72.3 Internationa
10、l Electrotechnical Commission (IEC)Documents:IEC Publication 60343 Recommended test methods for de-termining the relative resistance of insulating materials tobreakdown by surface discharges82.4 Institute of Electrical and Electronic Engineers (IEEE)Document:IEEE SS 11205-TBR Guide for the Statistic
11、al Analysis ofElectrical Insulation Voltage Endurance Data, 198793. Terminology3.1 For definitions of other terms used in this standard, referto Terminology D 1711 and Test Method D 1868.3.2 Definitions of Terms Specific to This Standard:3.2.1 threshold voltageThat voltage below which failurewill no
12、t occur under the test conditions irrespective of theduration of the test.3.2.1.1 DiscussionDemonstration of a threshold is diffi-cult when the slope of a volt-time curve is small, and failuretimes are long. High frequency tests are often an aid in1This test method is under the jurisdiction of ASTM
13、Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved March 10, 2001. Published May 2001. Originallypublished as D 2275 64 T. Last previous edition D 2275 95.2Annual Book of ASTM Standards, V
14、ol 10.01.3Annual Book of ASTM Standards, Vol 10.02.4Annual Book of ASTM Standards, Vol 14.04.5Annual Boof of ASTM Standards, Vol 11.03.6Annual Book of ASTM Standards, Vol 15.09.7Available from ASTM Headquarters, 1916 Race St., Philadelphia, PA 19103.8Available from American National Standards Instit
15、ute, 11 West 42nd St., 13thFloor, New York, NY 10036.9Available from IEEE Headquarters, 345 East 47th St., New York, NY 10017.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.demonstration, by reducing the time required to reach anece
16、ssary number of voltage cycles.3.2.2 voltage endurance, nThe time that an insulatingmaterial can withstand a prolonged alternating voltage stressunder the action of surface corona.3.2.3 voltage stress-time curve, nA plot of the logarithmof the mean or median time to failure of a material againstvolt
17、age stress (or the logarithm of voltage stress) for aparticular set of test conditions.3.2.3.1 DiscussionThe plot is the quantitative depiction ofthe voltage stress endurance over a range of voltage stress forthe conditions of test, and for the thickness tested. The curvesof a material obtained at t
18、wo thicknesses are different.3.2.4 volt-time curve, nA plot of the logarithm of themean or median time to failure of a material against voltage (orthe logarithm of voltage) for a particular set of test conditions.3.2.4.1 DiscussionThe plot is the quantitative depiction ofthe voltage endurance over a
19、 range of voltage for the condi-tions of the test, which includes the particular thickness tested.4. Summary of Test Method4.1 In this test method, voltage sufficient to produce coronais applied to the specimen until failure occurs. Comparativevoltage endurance is the relative time to failure of two
20、 differentmaterials of the same thickness when tested with similarelectrodes at the same voltage. Comparison is also possible interms of the magnitude of voltage stress (kV/mm or kV/in.)required to produce failure in a specified number of hours.4.2 Surface corona exists in the electrically stressed
21、gaswhere electrodes are near insulation surfaces.4.3 As with most tests at constant stress, there may be alarge dispersion of times to failure for a given sample. Themedian time of nine specimens (time of fifth failure) may beused as the failure time for the sample. This removes thenecessity of wait
22、ing for the last few to fail. The mean may alsobe determined statistically (see IEEE SS 11205-TBR for addi-tional information).4.4 Under the proper conditions, the test may be acceleratedby increasing the frequency of the applied voltage (seeAppendix X1).4.5 Standardized test conditions and conditio
23、ning prior totesting are important. In particular, tests with specified air flowat both low and moderate humidities may be informative. Inspecial cases, where a service condition is thought to alter thecorona endurance, this factor should be introduced as part ofthe test and reported. Such condition
24、s might include elonga-tion, elevated temperature, high humidity, other gases besidesair, pollution, etc.4.6 Additional information from the test may be obtained ifcorona-voltage levels and corona intensity are measured at thestart of the test and monitored at various stages of deteriorationof the i
25、nsulation. The voltage levels include corona-inceptionvoltage, corona-extinction voltage, and corona intensity usingTest Method D 1868. Also, comparative measurements ofcorona power or energy by bridge and oscilloscope techniquescan be informative (see ASTM STP 198 and STP 669).4.7 If elevated frequ
26、encies are used to accelerate the test, itis recommended that the corona-discharge pulse heights andenergy per cycle at the test frequency be compared with thesevalues at rated power frequency. If the energy per cycle is thesame, it can be concluded that failure time is inverselyproportional to freq
27、uency.5. Significance and Use5.1 This test method is used to compare the endurance ofdifferent materials to the action of corona on the externalsurfaces. A poor result on this test does not indicate that thematerial is a poor selection for use at high voltage or at highvoltage stress in the absence
28、of surface corona. Surface coronashould be distinguished from corona that occurs in internalcavities for which no standardized test has been developed.Evaluation of endurance by comparison of data on specimensof different thickness is not valid.5.2 The processing of the material may affect the resul
29、tsobtained. For instance, residual strains produced by quenching,or high levels of crystallinity caused by slow cooling mayaffect the result.Also, the type of molding process, injection orcompression, may be important especially if the mixing offillers or the concentration and sizes of gas-filled ca
30、vities arecontrolled in any degree by the process. Indeed, this testmethod may be used to examine the effects of processing.5.3 The data are generated in the form of a set of values oflifetimes at a voltage. The dispersion of failure times can beanalyzed using Weibull or extreme value statistics to
31、yield anestimate of the central value of the distribution and its standarddeviation. This is particularly recommended when the disper-sion of failure times is large, and a comparison of lifetimes oftwo materials must be made at a specified level of confidence.5.4 This test is often used to demonstra
32、te the differencesbetween different classes of materials, and to illustrate theimportance of eliminating corona in any application of aparticular material. When the test is used for such purposes orother similar ones, the need for precision is reduced, andcertain time saving techniques, such as trun
33、cating a test at thetime of the fifth failure of a set of nine, and using that time asthe measure of the central tendency, are recommended. Twosuch techniques are described in 10.2. Both techniques removethe necessity of testing beyond median failure, and reduce therequired testing time to approxima
34、tely half of that required toobtain failures on all specimens.5.5 Insulating materials operating in a gaseous medium aresubjected to corona attack at operating voltage on some typesof electrical apparatus in those regions where the voltagegradient in the gas exceeds the corona inception level. On ot
35、hertypes of equipment, where detectable corona is absent initially,it may appear later due to transient over-voltages or changes ininsulation properties attending aging. Certain inorganic mate-rials can tolerate corona for a long time. Many organicmaterials are damaged quickly by corona, and for the
36、se,operation with no detectable corona is imperative. This testmethod intensifies some of the more commonly met conditionsof corona attack so that materials may be evaluated in a timethat is relatively short compared to the life of the equipment.As with most accelerated life tests, caution is necess
37、ary inextrapolation from the indicated life to actual life under variousoperating conditions in the field.5.6 The failure produced by corona may be due to one ofseveral possible factors. The corona may erode the insulationD2275012until the remaining insulation can no longer withstand theapplied volt
38、age.The corona may cause the insulation surface tobecome conducting. For instance, carbonization may occur, sothat failure occurs quickly. On the other hand, compounds suchas oxalic acid crystals may be formed, as with polyethylene, inwhich case the surface conductance will vary with ambienthumidity
39、, and at moderate humidities the conductance may beat the proper level to reduce the potential gradient at theelectrode edge, and thus cause either a reduction in the amountof corona, or its cessation, thus retarding failure. The coronamay cause a “treeing” within the insulation, which mayprogress t
40、o failure. It may release gases within the insulationthat change its physical dimensions. It may change the physicalproperties of an insulating material; for instance, it may causethe material to embrittle or crack, and thus make it useless.5.7 Tests are often made in open air, at 50 % relativehumid
41、ity. It may be important for some materials to make testsin circulating air at 20 % relative humidity or less (seeAppendix X1). If tests are made in an enclosure, the restrictionin the flow of air or other gas may influence the results (seeAppendix X2).5.8 The shape of the (voltage stress)-(time-to-
42、failure) curveis sometimes useful as an indicator of the useable electricstrength of a material in an application involving surfacecorona and its variation with time of application of voltage,though such comparisons are risky. (Specimen thickness,electrode system, the presence of more than one mecha
43、nism offailure, and the details of the ambient, including the nature ofthe surface corona, all have significant effects.) For instance,on log-log paper, the volt-time curve often obtained by theprocedures of this test for void-free materials such as polyeth-ylene sheet generally has a continuous cur
44、vature that is slightlyconcave upward. The low voltage end of the curve tendstoward the horizontal and approaches a threshold voltagebelow which the curve does not go. A similar threshold wouldbe expected for many materials in an application involvingsurface corona. Moreover, if the material possess
45、es a lowelectric strength (as measured by Test Method D 149), orespecially if in service there is another mechanism of failure inthe short time range of this test, the shape of the left hand endof the curve would be affected and would not reach the samehigh levels of stress as are exhibited by polye
46、thylene either onthis test or in many service applications, including surfacecorona. In summary, voltage stress-time curves are useful toolsfor examining modes and mechanisms of failure, but must beused with care.5.9 For materials that possess a basic resistance to corona,such as mica, or, to a smal
47、ler degree, silicone rubber, the timerequired for the curve to reach the threshold produced bycorona may be greater by many orders of magnitude than thetime required for materials such as polyethylene, polyethyleneterephthalate, or polytetrafluoroethylene.5.10 The variability of the time to failure
48、is a function of theconstancy of the parameters of the test, such as the testvoltages, which should be monitored. It is also a significantmaterial property. The Weibull slope factor, b, is recommendedas a measure of variability. b is the slope obtained whenpercent failure is plotted against failure
49、time on Weibullprobability paper. Such a plot is called a “Weibull probabilityplot” (see Fig. 1).5.11 The shape of the Weibull probability plot can provideadditional information. A non-straight-line plot may indicatemore than one mechanism of failure. For instance, a fewunaccountably short time failures in the set could indicate asmall portion of defective specimens with a different failuremechanism from the rest of the lot.6. Apparatus6.1 Electrical Circuit:6.1.1 High-Voltage SupplyA high-voltage source withcontrols and voltage-measuring means in accordance withrequirements
